1. Field of the Invention
This invention relates to an apparatus and a method for sensing an electric current flowing through an electric circuit assembled into various instruments and devices of, for example, an automobile, and particularly to an apparatus and a method for sensing an electric current using a magneto-electric conversion element.
2. Description of the Related Art
Electric current sensors for sensing an electric current using hall elements are conventionally known. Hall element is a type of magneto-electric conversion elements. One example of such electric current sensors is disclosed in Japanese Patent Application Laid-open No.62-98267.
FIG. 1 illustrates the electric-current sensor disclosed in 62-98267. A first hall element 115 is placed in the gap defined by the two end faces 112 and 113 of the C-shaped magnet 114. A conductor C extends perpendicular to the plane defined by the C-shaped magnet 114. The first hall element 115 is placed so that its magnetism-sensitive surface is perpendicular to the magnetic field created by the magnet 114. The first hall element 115 produces an electromotive force in response to a small amount of electric current flowing through the conductor C.
A second hall element 116 is placed apart from the magnet 114 at a predetermined distance and adjacent to the conductor C, with its magnetism-sensitive surface is perpendicular to a magnetic field induced by the electric current flowing through the conductor C. In other words, the second hall element 116 feels the magnetic field induced by the electric current, but is not so affected by the magnetic field produced by the magnet 114 as the first hall element 115.
An electromotive force becomes large as an electric current increases as long as magnetic flux is not saturated. Accordingly, with this electric current sensor, if the electric current flowing through the conductor C is small, the first hall element 115 is used. If the electromotive force of the first hall element 115 is being saturated, then, the electromotive force of the second hall element 116 is used to detect the electric current. This arrangement improves the accuracy of the sensing ability, and at the same time, increases the range of detection.
FIG. 2 illustrates another prior art technique, which is an electric current sensor disclosed in Japanese Patent Application Laid-open No. 8-194016. A busbar 121 is bent into a U-shape to form a return conductor 122. The return conductor 122 has legs 121a and 121b, each of which has a center line that is coincident with one of the current center lines Ia and Ib. Magnetic sensors 123a, 123b, and 123c are arranged along a line 124 which is perpendicular to a plane that contain the current center lines Ia and Ib and passes in the middle between the legs 121a and 121b. The distances from the return conductor 122 to the three magnetic sensors 123a, 123b, and 123c are different.
The outputs of the magnetic sensors 123a, 123b, and 123c are saturated if the intensity of a magnetic field exceeds a predetermined value. The magnetic field induced by the electric current I flowing through the return conductor 122 is sensed by one of the magnetic sensors 123a, 123b, and 123c. If a small quantity of electric current flows through the return conductor 122, the magnetic sensor 123a positioned closest to the legs 121a and 121b is used to detect the electric current. To measure a large quantity of electric current, the magnetic sensor 123c remote from the legs 121a and 121b is used. With this arrangement, the intensity of the magnetic field can be measured in an appropriate range, regardless of the level of the electric current being measured.
Both types of electric current sensors disclosed in 62-98267 and H8-194016 148 improve the resolution of current measurement and broaden the range of the measurable current. However, both require two or more magneto-electric conversion elements (i.e., hall elements), which causes the manufacturing cost for a current sensor to be high.
In addition, the solid properties, such as a temperature property, a sensitiveness property, an offset-drift property, and so on, of magneto-electric conversion elements vary from one another, and such variations have to be corrected in actual use.
Furthermore, both types of current sensors require a signal selector for selecting one of signals supplied from the multiple magneto-electric conversion elements. This requirement inevitably makes the hardware scale of the electric-current sensor large.
Therefore, it is an object of the invention to overcome these problems in the prior art, and to provide an apparatus and a method for sensing a broad range of electric current at a high precession and a low cost, using a single magneto-electric conversion element.
In order to achieve the object, in one aspect of the invention, an electric current sensor detects an electric current flowing through a conductor, making use of magnetic flux induced about the conductor by the electric current flowing through the conductor. The electric current sensor comprises a single magneto-electric conversion element having a magnetic-flux sensitive surface, and an angle adjusting mechanism for changing the angle between the magnetic-flux sensitive surface of the magneto-electric conversion element and the direction of the magnetic flux induced by the electric current. The magneto-electric conversion element is, for example, a hall element, which outputs an electric signal in response to the magnetic flux density at the magnetic-flux sensitive surface. The electric current sensor detects the electric current flowing through the conductor based on the electric signal output from the magneto-electric conversion element whose magnetic-flux sensitive surface is oriented with respect to the magnetic flux at a selected angle.
The electric current sensor has a junction box for accommodating a portion of the conductor and having a hole on one face, and a cock fit into the hole in a removable manner. The cock supports the magneto-electric conversion element, and the magneto-electric conversion element is placed inside the junction box when the cock is fit into the hole of the junction box. The cock is rotated with respect to the hole of the junction box. The circumference of the hole and the periphery of the cock constitute the angle adjusting mechanism.
Preferably, the hole has a plurality of recesses at a predetermined interval around the circumference. Each recess extends in the radial direction from the circumference of the hole so as to define a contour of gear teeth. The cock has a plurality of teeth at a predetermined interval along its periphery. In this case, the angle adjusting mechanism comprises the teeth of the cock and the recesses of the hole, which are meshed with and disengaged from each other.
Alternatively, the hole has an internal thread, and the cock has an external thread. In this case, the angle adjusting mechanism comprises the external thread of the cock and the internal thread of the hole.
In another aspect of the invention, an electric current sensor for sensing an electric current flowing through a conductor comprises a clipping frame having a slit and two wings separated by the slit. The conductor is inserted in the slit and clipped by the two wings of the clipping frame. In this state, if the electric current flows through the conductor, a magnetic flux is induced about the conductor. A pair of hall elements is placed inside the respective wings of the clipping frame, each hall element having a magnetic-flux sensitive surface. The electric current sensor also includes an angle adjusting mechanism for changing the angle of the magnetic-flux sensitive surface of the hall element with respect to the direction of the magnetic flux.
Preferably, a pair of angle-adjusting projections is formed in the inner faces of the slit, and multiple angle-adjusting holes are formed in the conductor at a predetermined interval along an arch. When the electric current sensor is attached to the conductor, the pair of angle-adjusting projections are fit into one of the angle-adjusting holes. In this case, the pair of angle-adjusting projections and the plurality of holes constitute the angle adjusting mechanism.
Alternatively, a pair of angle-adjusting recesses is formed in the inner faces of the slit, and multiple angle-adjusting projections are formed in the conductor at a predetermined interval along an arch. When the electric current sensor is attached to the conductor, the pair of angle-adjusting projections are fit into one of the angle-adjusting holes. In this case, the pair of angle-adjusting projections and the plurality of holes constitute the and adjusting mechanism.
Alternatively, a pair of angle-adjusting recesses is formed in the inner faces of the slit, and multiple angle-adjusting projections are formed on the conductor at a predetermined interval along an arch. One of the angle-adjusting projections is fit into the angle-adjusting recesses when the electric current sensor is attached to the conductor. IN this case, the pair of angle-adjusting recesses and the plurality of angle-adjusting projection the angle adjusting mechanism.
In still another aspect of the invention, a method for sensing an electric current flowing through a conductor is provided. The electric current flowing through the conductor induces a magnetic flux about the conductor. With the method, first, a magneto-electric conversion having a magnetic-flux sensitive surface is placed in the magnetic field. Then, the orientation of the magnetic-flux sensitive surface is oriented with respect to the direction of the magnetic flux. The magneto-electric conversion element is caused to output an electric signal in response to a magnetic flux density at the magnetic-flux sensitive surface. Finally, the electric current flowing through the conductor is measured based on the electric signal output from the magneto-electric conversion element.